The present invention relates to a graphics display method and apparatus and particularly to such method and apparatus wherein a viewport is panned within a larger virtual screen area employing a movable cursor.
A known apparatus for providing a graphics computer terminal display includes a cathode-raytube portraying an image which is refreshed from a pixel bit map memory wherein each of the elementary bits of the image are stored. There is not always a one-to-one relationship between the information represented on the cathode-ray-tube screen and the size of the pixel bit map memory from which the screen information is derived. Thus, the pixel bit map memory may represent a larger virtual screen while the cathode-ray-tube presentation represents a window or viewport into the larger virtual screen. That is the cathode-ray-tube image is a visible version of part of the virtual screen stored in memory. In such case, more than one screen presentation may be simultaneously stored in memory and the visual presentation on the screen can be switched between the blocks of stored information. Although some selection can be made relative to the portion of the virtual screen which is to be displayed, the prior art did not provide a convenient way of "panning" the viewport window with respect to the virtual screen stored in memory.